The present invention relates to a metal laminate gasket which includes two outer plates and one intermediate plate, specifically, the invention relates to the metal laminate gasket wherein secondary seal is strengthened around a seal hole.
Metal laminate gaskets, formed by laminating metal plates with seal means, have been used as gaskets for a connection portion between a cylinder block and a cylinder head of an internal combustion engine, other connection portions of internal combustion engine, and connecting portions of pipes.
In the internal combustion engines for automobiles, especially recent small-sized, light weight and high power engines, the size and weight of an engine are reduced, and a cylinder head and a cylinder block are formed with aluminum alloy with relatively weak rigidity. As a result, there is a tendency that rigidity of the engine decreases. Therefore, for sealing the gasket, if only a primary seal of a conventional cylinder hole (cylinder bore) is increased, for a recent engine which has factors that cause deformation of the engine, gas leak may be enhanced. Especially, deformation of the cylinder head becomes a problem as pressure rises inside the cylinder in the high powered engine.
The deformation of the cylinder head is small near a tightening bolt, and as the distance from the bolt is increased, the deformation becomes great, and as the distance is closer to the center of the cylinder bore wherein a large combustion pressure operates, deformation becomes great.
Following the deformation of the cylinder head, in order to obtain enough seal efficiency, it is necessary to provide not only the primary seal, but also the secondary seal effectively around the cylinder bore hole. Especially, in considering a partial deformation around the cylinder bore, since deformation of the center side is larger and a peripheral side is smaller, it is important to obtain a surface pressure distribution where a seal surface pressure is large at an inner side and gradually becomes smaller towards to the peripheral side so as to follow such inclined deformation.
On the other hand, regarding the metal laminate gasket, followed by a reduction in size, weight, and cost of the engine, number of lamination is reduced and also an adaptable seal method is simplified. As a relatively simple structured metal laminate gasket, there is a gasket composed of two surface plates and one intermediate plate.
For the metal laminate gasket formed of three metal plates, several cylinder head gaskets were formed wherein secondary seal was gradually increased to handle a partial deformation of the cylinder block and cylinder head of a small engine.
The cylinder head gasket is provided, for a seal hole such as cylinder bore, with a primary seal and a secondary seal outside the primary seal, wherein in the surface pressure distribution of the secondary seal, inside thereof is the largest, and the outside becomes gradually smaller.
For this example, a metal laminate gasket shown in FIG. 8 and modified metal laminate gasket shown in FIG. 9 were examined.
For these metal laminate gaskets, a first bead is formed in an inner peripheral side of a shoulder portion of a first surface plate to form a primary seal. In order to protect the first bead from the high heat combustion gas, a second surface plate is folded back, and a circumferential edge of the folded plate is opposed with the shoulder of the first surface plate.
Also, to form the secondary seal, a second bead 71 (FIG. 8) is formed in an intermediate plate 70 for conventional gasket in FIG. 8 and FIG. 9, and a shim 80 (FIG. 9) is placed on the intermediate plate 70A. In order to provide the intermediate plate 70 and 70A between the first surface plate 50 and second surface plate 60, a shoulder 52 is formed between the first bead 51 and second bead 71 in the first surface plate 50.
However, for the metal laminate gaskets 5, 5A in FIG. 8 and FIG. 9, it is impossible to generate large surface pressure on the shoulder 52 by tightening the gasket 5 and 5A because the first bead portion 51 is disposed under a folding portion 61 of the secondary surface plate 60 by gradually bending the shoulder 52 of the first surface plate 50.
Therefore, in the secondary seal strengthening method, as shown in the surface pressure distribution in FIGS. 8 and 9, it becomes a mountain type where a large surface pressure is in the center or a rectangular type with plain surface pressure. As shown in FIG. 10, like a recent cylinder head with relatively small rigidity, a center side of the cylinder bore 2 separates from the cylinder block 9 and this deformation becomes smaller toward the outside of the cylinder bore 2. In other words, there is a problem that enough seal effect can not be obtained when deformation with inclination occurs.
On the other hand, the present inventor proposed a metal laminate gasket, wherein in a shoulder portion of a first outer plate which is located close to a folding back portion of a second outer plate, a bending portion is formed by bending the first outer plate in a step form to have a clank or z-shape in a cross section to thereby generate a large seal pressure at the shoulder portion (for example, refer to Patent Publication 1). This method is applied to the invention.
Patent Publication 1: Japanese Patent Publication No. 10-38086.
In view of the problems described above, an object of the present invention is to provide a metal laminate gasket which can generate a primary seal generated at a first bead located inside a folding back portion surrounding a seal hole, and a secondary seal which has a pressure distribution with high peak from the inner side to the outer side around the primary seal.
Further objects and advantages of the invention will be apparent from the following description of the invention.